1. Field of the Invention
The present invention relates to a housing structure having a main body structure and a cover structure, equipment being housed in the main body structure and the cover structure, and to an image forming apparatus such as a printer having the housing structure, a copying machine, a facsimile, a digital composite machine, and the like.
2. Description of the Related Art
Conventionally, an image forming apparatus having a writing unit by use of a laser beam has been known. In such an image forming apparatus, generally, the writing unit is fixed in a main body of the image forming apparatus. However, in such a system, a photoconductive drum unit is required to pass around the writing unit when the photoconductive drum unit is installed in or removed from the main body so that low operability for changing parts and large size of the apparatus are caused. Then, technology for solving the above problems is disclosed in, for example, Japanese Patent Application Publication Nos. H05-323686 and H02-210462.
In Japanese Patent Application Publication No. H05-323686, the main body of the image forming apparatus consists of an upper structure and a lower structure. The upper structure is disposed to be openable and closable about a supporting point on the lower structure and a coil spring is provided at the supporting point to bias the upper structure in an opening direction. When the upper structure is opened, a direction of gravity affecting the upper structure is switched from an opening direction to a closing direction of the upper structure through a position of the supporting point. The housing structure includes an impact absorbing elastic member for absorbing an impact occurring when the upper structure is in an opened position based on the gravity. Thereby, even when the upper structure is in the opened position based on the gravity, the impact absorbing elastic member can prevent the lower structure from being affected by a large impact and from the characteristics of parts provided in the apparatus from being affected by the influence of a large impact.
In Japanese Patent Application Publication No. H02-210462, an image forming unit includes positioning members having the same shape as each other at both sides of the image forming unit. The positioning member has, at one side, a first shaft portion for supporting a photoconductive drum and a second shaft portion for supporting a roller, and, at the other side, an engagement portion disposed coaxially with the first shaft portion. The image forming unit is positioned on the main body through the engagement portion. Thereby, a driving gear of the photoconductive drum can be highly accurately engaged with a driving system of the main body.
In Japanese Patent Application Publication No. H05-323686, it is disclosed that, when the upper structure including the writing unit is closed onto the lower structure, a pressing-up spring is provided for applying a biasing force in a direction opposite to the closing direction of the upper structure. The biasing force of the pressing-up spring is applied when a distance between the lower structure and the upper structure reaches a predetermined value or less.
In Japanese Patent Application Publication No. H02-210462, the writing unit is fixed on the upper cover and rotated. The upper cover is biased in the opening direction and any impact occurring when the writing unit is closed is absorbed.
Although both of Japanese Patent Application Publication Nos. H05-323686 and H02-210462 disclose the use of the elastically biasing force when the upper cover structure is closed, there is a problem of accurate positioning of the writing unit. If the writing unit is supported in a floating state in the upper cover and then positioned on the main body, it may be possible to use a damper for reducing the closing speed of the upper cover, but this is costly. In addition, the positioning portion of the writing unit and the main body of the image forming apparatus is commonly made of a hard material such as a resin including glass, or the like and therefore impact occurs when the hard materials collide with each other.